This invention deals generally with loop heat pipe evaporators, and more specifically with increasing the heat transfer from the location of heat input to the evaporator.
One of the limitations for loop heat pipes is related to the heat input to the evaporator. Conventional loop heat pipe primary wicks have a heat flux limit at approximately 25 W/cm2. Excessive heat flux causes boiling inside the wick, which disrupts liquid return flow and results in unstable operation of the loop heat pipe and dry-out.
The maximum heat flux in the evaporator wick and typically in the entire loop heat pipe system is found at the interface between the wick and evaporator casing. At this location, heat transfer can occur by two paths, by conduction through the liquid—saturated wick or by convection of the vapor in the vapor grooves that are along the casing inner surfaces and/or the wick outer surfaces. To transfer heat by convection the vapor must collect the heat from the evaporator casing and then deposit this heat in the wick. This is a poor heat transfer path because of the relatively low convective heat transfer coefficient of the vapor flow. Conduction requires heat to move from the location of heat input through the evaporator casing directly to the liquid-saturated wick and is a much more favorable method. However, the vapor grooves are located between the wick and evaporator casing. As a result, they reduce the heat transfer area available for conduction. This reduction in area concentrates heat flux, and as a result the highest heat flux occurs at this point. This problem is aggravated by non-uniform heat flux distribution, which further concentrates the heat flux. To increase the heat flux tolerated at the heat input location of the loop heat pipe, this heat flux concentration needs to be reduced.
Therefore the purpose of the present invention is to produce a more uniform heat flux at the interface between the loop heat pipe wick and evaporator casing.